1. Field
The present invention relates to a transmission delay analyzing apparatus, a medium recording a transmission delay analyzing program, and a transmission delay analyzing method that analyze a variation in transmission delay caused by noise.
2. Description of the Related Art
There is known an analysis technique that uses a simulator for checking whether a signal is normally transmitted in a device that exchanges information in high-speed signal transmission. Whether such an information communication device is operating normally or not is determined using a timing calculation of a signal transmitted between an LSI (Large Scale Integration). Since the timing calculation is performed with a delay variation taken into consideration, simulation needs to be used to calculate this value.
A transmission waveform changes under the influence of crosstalk noise generated by crosstalk between transmission lines. The delay variation is defined as the maximum and minimum values of the difference between a transmission delay at the time of absence of influence of crosstalk and transmission delay at the time of presence of influence of crosstalk.
The reason for using the maximum and minimum values is that the difference between a transmission line delay at the time of absence of influence of crosstalk and transmission line delay at the time of presence of influence of crosstalk changes depending on the timing at which crosstalk exerts an influence on the transmission line. Here, the maximum value indicates the largest value of the transmission line delay, and the minimum value indicates the smallest value thereof.
An example of a conventional delay variation calculation method which uses a waveform synthesis technique will be described.
A procedure of calculating the delay variation is as follows.
(S1) A simulator generates a transmission waveform free from crosstalk noise and measures a transmission line delay with respect to the transmission waveform with a voltage VIH or VIL set as a threshold.
(S2) The simulator generates a crosstalk noise waveform.
(S3) The simulator generates another transmission waveform by superimposing, at a predetermined timing, the crosstalk noise waveform on the crosstalk-noise-free transmission waveform and measures the transmission line delay with respect to the transmission waveform with a voltage VIH or VIL set as a threshold.
(S4) The simulator changes the timing at which the crosstalk noise waveform is superimposed on the crosstalk-noise-free transmission waveform and executes once again the processing of S3 for measuring transmission line delay data.
(S5) The simulator calculates a difference between the transmission line delay measured in S1 and that measured in S3 and a difference between the transmission line delay measured in S1 and that measured in S4 and sets the maximum value and minimum value of the calculated differences as the delay variation.
As a prior art relating to the present invention, there is known an input buffer circuit capable of outputting a stable signal even if noise is included in an input signal (refer to, e.g., Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 7-264041)
However, in the conventional delay variation calculation method, it is necessary to generate a plurality of transmission waveforms by superimposing the crosstalk noise waveform on the crosstalk-noise-free transmission waveform and to measure the transmission line delay for each generated transmission waveform. Therefore, it takes time to calculate the delay variation.